Liquid Crystalline Aromatic Polyesters molecular weight

It was, however, observed that such systems under appropriate conditions of concentration, solvent, molecular weight, temperature, etc. form a liquid crystalline solution. Perhaps a little digression is in order here to say a few words about liquid crystals. A liquid crystal has a structure intermediate between a three-dimensionally ordered crystal and a disordered isotropic liquid. There are two main classes of liquid crystals lyotropic and thermotropic. Lyotropic liquid crystals are obtained from low viscosity polymer solutions in a critical concentration range while thermotropic liquid crystals are obtained from polymer melts where a low viscosity phase forms over a certain temperature range. Aromatic polyamides and aramid type fibers are lyotropic liquid crystal polymers. These polymers have a melting point that is high and close to their decomposition temperature. One must therefore spin these from a solution in an appropriate solvent such as sulfuric acid. Aromatic polyesters, on the other hand, are thermotropic liquid crystal polymers. These can be injection molded, extruded or melt spun. 

A common method for polyester formation is via trans-esterification. The procedure described below uses a procedure that is modified from that described in Sorenson. In this case, aromatic di-acid 5 and di-ester 4 monomers are reacted together in the melt. During the polymerization, the molecular weight grows while volatile side-product is continuously removed from the reaction vessel by means of a vacuum pump. Scheme 2 describes the formation of a main-chain liquid crystalline poly(ester ether) containing... 

Low-molecular-weight liquid-crystalline compounds have been known for about 100 years. However, main chain liquid crystal polymers (MCLCPs) have attained prominence only in the last 15 years. In 1956 Flory predicted lyotropic behaviour and this theoretical prediction was well demonstrated in the synthetic polymer area with the discovery by Kwolek of the aramids, e.g. poly(/ -phenyleneterephthamide). This led to interest in thermotropic main chain LCPs and, although aromatic polyesters which are thermotropic were described during this period in patents issued to and Carborundum Co., their liquid-crystalline... 

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